This invention is directed to an arterial blood filter specifically designed for use in extra-corporeal blood bypass circuits as are often used in cardio-pulmonary surgery.
One type of blood filter in the prior art is the type that may be used for slow flow and single pass filtration such as for the filtering of blood from blood bank bags or intravenous solutions. These filters have large pores and mainly filter out clots and large debris. However, in the filtration of blood in an extra-corporeal blood circuit employed during open-heart surgery, there are relatively high flow rates going up to 6.5 liters per minute (and repeated recirculation of the blood through the circuit).
At present, there are two kinds of filters used for extra-corporeal blood circuit filtration in the cardio-pulmonary bypass situations. One is sold by Swank and is the form of a filter which has matted fibers in a 3-dimensional structure to provide a depth filter. The fibers may have a sticky surface so that the blood elements may adhere to it. In some cases, this kind of filter plugs up fast and restricts or stops blood flow. Furthermore, when the filter is of a depth construction, it is more likely to filter out even the desirable blood elements such as white cells.
Another available filter is basically a single layer woven filter screen of approximately 20 to 50 micron pore size. This filter has a single surface interposed in the blood flow stream. A surface area of approximately 100 square inches is employed for the intended flow. Sometimes, the filter material is metallic wire, and sometimes it is polymer composition material. In the case of polymer composition material, it may or may not be thermoplastically bonded at the crossover points. Furthermore, the prior patents speak of both simple weaving and twill weaving of the strands. Such filters are available from the Pall Corporation of Glen Cove, N.Y., as exemplified by Rosenberg U.S. Pat. No. 3,696,932 and Krakauer et al. U.S. Pat. No. 3,701,433. Such filters are also available from Johnson and Johnson, New Brunswick, N.J. as exemplified by Mouwen et al. U.S. Pat. No. 4,056,476. These companies appear to be the present principal suppliers of disposable blood filters used for extra-corporeal blood bypass circuits.
However, such blood filters have functional problems so that there is room for substantial improvement as becomes clear from the description of the blood filter of this invention.